1. Field of the Invention
The present invention relates to magnetic lifting devices and, more particularly, to an improved hydraulically controlled magnetic lifting device for use with crane-type apparatus.
2. Description of the Prior Art
Various magnetic lifting devices have been proposed for use as attachments to different types of equipment; as, for example, cranes and the like. Such devices have generally been of the permanent magnet or electromagnet type and have been designed for lifting metallic objects, such as scrap metal and other objects of various weights and dimensions. The versatility of these devices for use in any particular situation with a variety of loads has been restricted by the need for specialized and complex control attachments to govern the lifting force and movement of the magnets.
By way of example, in devices employing permanent magnets, a variety of complex controls have been required to mechanically regulate the permanent magnet to enable the load and release. These controls are expensive, limited in their effectiveness, and usually require that the equipment undergo substantial modification prior to use.
In lifting equipment employing electromagnets, a primary source of electrical power is required to control magnetic attraction and release. Magnetic lifting devices of this type, therefore, may not be used without providing a separate or additional source of electrical power on the existing equipment.